1. Field of the Invention
The present invention relates to piezoelectric speakers using piezoelectric elements.
2. Description of the Related Art
Conventionally, there are piezoelectric speakers in each of which an electrode of a piezoelectric ceramics plate is divided so as to planarize peaks and dips of sound pressure frequency characteristics caused by resonance (for example, see Japanese Unexamined Patent Application Publication No. 5-122793). FIG. 12 is a diagram showing a conventional piezoelectric speaker disclosed in JP 5-122793.
In FIG. 12, the conventional piezoelectric speaker is equipped with a piezoelectric sounding body 1 and a frame 2 for supporting an outer peripheral portion of the piezoelectric sounding body 1. The piezoelectric sounding body 1 includes a round piezoelectric ceramics plate 3 and a metal plate 4 joined to the piezoelectric ceramics plate 3. Moreover, electrodes formed on both faces of the piezoelectric ceramics plate 3 are divided at a location determined by a high-order resonance mode. Then, a voltage lower than a voltage applied to an inside electrode 5a is applied to an outside electrode 5b located outside the position where the electrodes are divided. A technique disclosed in JP 5-122793 controls a resonance mode generated in the piezoelectric sounding body 1 by variation in the applied voltage in this way. With this, the technique disclosed in JP 5-122793 improves the peaks and dips of the sound pressure frequency characteristics.